Platform scales are well known in the art and are utilized for many different purposes. For examples, platform type scales are used in commercial grain operations for measuring the amount of grain brought to an elevator. Similarly, states utilize platform scales to measure the weight of semi-trailer and tractor units to determine whether or not such units are complying with state laws which regulate highway loads.
The scales may be either mechanical or electronic scales. In either event, the scales often have a plurality of individual scale platforms, for example, a series of three platforms. By mechanical linkage or by electronic load cells, as a vehicle rests on one or more of the platforms, the weight is indicated by the scale.
It is not unusual for such platform scales to measure vehicles and their loads weighing as high as 20 tons and in some cases, as high as 100 tons. Dirt and friction have a tendency to build up at critical points in mechanical scale mechanisms and slow the action of the pivots. Similarly, adjustment drift often has the same effect on electronic scales. In either event, it takes extra weight to reach a given point on the scale indicator or scale readout. Therefore, when this occurs, the scales have a tendency to read a lower weight than the actual weight. Accordingly, the prior art has recognized for a long time that it is important to calibrate platform scales. It is also well known that calibrations will vary even on the same scale at different loadings. Therefore, state agencies often require platform scales to be calibrated at loadings sometimes as high as twice their rated capacities.
In the past, platform scales were tested by placing individual unit weights, normally either 500 pound units or 1,000 pound units, upon the individual platform sections of a platform scale. It was not unusual to have two men spend a considerable amount of time in unloading, testing the scale, and reloading the uniform weights which were carried to the scale site by a vehicle.
It was also known in the prior art to actually drive a vehicle upon an individual segment or section of a platform scale. However, because the individual length of a scale section is approximately 9 feet long, the test vehicle was required to have a relatively short wheel base, somewhere around 100 inches, so that the wheels of the prior art vehicle would rest entirely upon the scale platform being tested. Therefore, such a scale testing vehicle was only suitable with respect to very small scales. If, for example, the vehicle was loaded with uniform weights to the amount necessary to properly load a high rated platform scale section, the test vehicle itself could be in violation of many state highway loading statutes, particularly with respect to bridge loading restrictions.